Device for mounting biased element in waveguide



Nov. 5, 1968 D. NEUF 3,409,849

DEVICE FOR MOUNTING BIASED ELEMENT 1N WAVEGUIDE Filed Nov. 8, 1965 5 Sheets-Sheet 1 PERMISSABLE REGION FOR LONG ITUDINAL SLOT INVENTOR. DONALD NEUF Nov. 5, 1968 D. NEUF 3,409,849

DEVICE FOR MOUNTING BIASED ELEMENT IN WAVEGUIDE I Filed Nov. 8, 1965 5 Sheets-Sheet 2 INVENTOR. DONALD NEUF ATTORNEYS Nov. 5, 1968 D. NEUF 3,409,849

DEVICE FOR MOUNTING BIASED ELEMENT IN WAVEGUIDE Filed Nov. 8, 1965 3 Sheets-Sheet 5 j INVENTOR. DONALD NEU F ATTORNEYS United States Patent 3,409,849 DEVICE FOR MOUNTING BIASED ELEMENT IN WAVEGUIDE Donald Neuf, Wantagh, N.Y., assignor to Control Data Corporation, Melville, N.Y., a corporation of Minnesota Filed Nov. 8, 1965, Ser. No. 506,698 4 Claims. (Cl. 333-98) ABSTRACT OF THE DISCLOSURE An element to be biased is mounted in a waveguide section which is split longitudinally with the slots in the top and bottom walls of the waveguide being offset from each other so that when the element is mounted across the short waveguide dimension it contacts both of the waveguide sections. Since the two sections are insulated from each other, a DC voltage can be applied to the respective sections and thus across the element. The split waveguide may be connected by choke joints to a stand ard waveguide.

The present invention relates to apparatus for mounting an element in a waveguide wherein a biasing voltage is to be applied to the element.

There are a number of known situations where it is desired to mount an element such as a probe or the like in a waveguide while applying a small direct biasing voltage across the element. For example, such biasing arrangements are frequently desirable with parametric amplifiers and various types of microwave switches.

Since waveguide is made of an electrically conductive continuous or closed material, and is not conducive to being insulated, a problem arises in applying a direct voltage across the mounted element without destroying important basic characteristics of the guide. The prior art has suggested several techniques to solve this problem. In one, a bypass capacitor is inserted between one of the waveguide walls and the mounted element. Because the size of the capacitor must be much less than one wavelength at the operating frequency, for higher frequencies it becomes increasingly difiicult to construct a capacitor with the low reactance required, and such devices have not performed reliably.

A second technique involves the use of a coaxial line which is built into the wall of the waveguide. The length of the coaxial line is made equal to an even number of quarter wavelengths of the frequency of interest, and it is therefore possible to obtain very low impedance at the opposite end of the line where the element is mounted. However, since the impedance reflected by the coaxial line is a function of the operating frequency, it does not remain constant. Moreover, it is difiicult to obtain a low impedance coaxial line, free from higher order modes at high frequencies to keep the reflected impedance of the line low.

The present invention overcomes these problems and provides a mechanically simple, broad band device wherein an element is mounted in a waveguide so that a biasing voltage can easily be applied across the element. Briefly, in accordance with the invention, a short waveguide is split longitudinally, depending upon the propagation mode employed, so that the current flow in the guide is not appreciably interrupted. Within certain tolerances, the slots in the opposing sections of the guide may be offset slightly so that a transverse element may be mounted in the guide and electrically connected to the opposite sections. Since the two sections of the waveguide are electrically insulated from each other by the slots, the application of the desired voltage across the two Waveguide sections will provide the desired bias across the element. A conventional choke r9 CC joint suitably insulated may be used to physically connect and electrically isolate the split waveguide from the remainder of the waveguide circuitry.

The invention is described in detail with reference to the following drawings, wherein:

FIG. 1 is a diagram showing the current flow in the walls of a waveguide for a particular propagation mode;

FIG. 2 is an exploded perspective view of the device according to the invention; and

FIG. 3 is a side cross-sectional view of the invention.

Referring to FIGURE 1, a typical waveguide is shown consisting of top and bottom walls 10 and 12 and opposing side walls 14 and 16 and made of an electrically con ductive material, Electromagnetic Waves may be propagated in the waveguide in an infinite number of modes, each such mode having a distinctive field pattern defining the electric and magnetic fields in the waveguide. The field patterns for a wide variety of different modes are well known in the microwave arts.

Moreover, depending upon any mode of propagation, a current flow will exist in the walls of the waveguide. In FIG. 1, the unnumbered lines with arrows represent the current flow in the walls 10 and 14 of the waveguide for the common TE mode. Although only the fiow of current in walls 10 and 14 is illustrated in FIG. 1, the current flow in walls 16 and 12 will also be substantially as shown with the arrows appropriately directed to provide continuity.

Examination of the current distribution in the conductive walls of the waveguide indicates that in the top and bottom walls 10 and 12 respectively, the current flows longitudinally of the waveguide axis at the geometric center of the walls as shown by line 18. It therefore follows that if a physically thin slot were cut in the center of walls 10 and 12, no appreciable losses would be introduced into the guide since current flow would not be interrupted and would merely flow on either side of the slot. Moreover, from a practical view point, it is not necessary that this slot be in the direct geometric center and it may be possible to place the slot in a zone such as defined by the area 20 without introducing any appreciable loss into the guide.

According to the invention and referring to FIGURES 2 and 3, a short waveguide 22 is longitudinally split into two sections 23 and 24 which are separated by offset splits 26 and 28. Thus, waveguide section 23 consists of a short upper wall portion 29, side wall 30 and a long lower wall portion 31. Waveguide section 24 consists of a long upper wall portion 32, side wall 33 and a short bottom wall portion 34. The element to be mounted 36 is shown connected between the long upper wall portion 32 and the long bottom wall portion 31. Negative and positive terminals 38 and 40 respectively, are connected to the waveguide sections 23 and 24, and adapted to be connected in a suitable fashion across a source of direct voltage (not shown) to bias the mounted element 36. For purposes of structural rigidity, the slots 26 and 28 may be filled with an epoxy or the like to secure the parts in the desired relationship. The slots should be as thin as possible to provide the necessary electrical insulation between sections 23 and 24.

Slots 26 and 28 are offset by an amount proportional to the width of the zone 20 illustrated in FIG. 1. This width may be derived empirically depending upon various parameters such as frequency, the particular waveguide and mode of propagation, and ultimate use of the device. Obviously, the smaller the zone, the less the current flow in the waveguide is interrupted, but the slots 26 and 28 must be offset a suflicient distance to permit mounting the element 36 in sections 23 and 24. If element 36 may be slanted or constructed in a staircase fashion, then it may be possible to avoid offsetting the slots 26 and 28,

however, in practice it has been found that excellent results are yielded when the slots 26 and 28 are displaced a distance less than ten percent of the internal guide width.

Since it is necessary that the sections 23 and 24 be electrically isolated from each other, they obviously cannot be directly coupled to conventional waveguide. However, conventional techniques may be employed for the required coupling. For example, if it is desired to insert the split waveguide section between two waveguides 44 and 46, the waveguides 44 and 46 may be connected to conventional choke joints 48 and 50 respectively. Such choke joints are well known and the theory of operation need not be described herein in detail. Each choke joint includes a circular groove 52 concentrically located with respect to the mouth of the waveguide. The depth of the groove may be equal to one quarter the wavelength of the fragmentary at the center of the frequency band with which the device is to be employed. The groove may be positioned with respect to the mouth of the waveguide so that the maximum distance from one of the rectangular edges (shown as 56 in FIG. 2) will be equal to one quarter wavelength at this center frequency. As is known, the choke joints function such that the impedance at the junc tion of the choke joints and respective waveguides 44 and 46, looking out, is substantially zero for slight separation. Hence, the walls at the joints appear continuous.

Each of the choke joints 48 and 50 is covered with a respective layer of insulation 58 and 60 such as Teflon and secured by screws or the like (not shown) to hold the split waveguide section in place. If the Teflon layer is made thin, for example, .0005 inch, the device will be operable over a wide band of frequencies. For example, the apparatus illustrated has been tested at 35, 60, 90 and 100 GH (1000 megacycles).

Many modifications of the invention will be obvious to those skilled in the art. The purpose of the choke joint is to provide smooth coupling of the electromagnetic energy between the waveguides 44 and 46 and also to provide a convenient way of electrically insulating the waveguide sections 23 and 24. Any other device for accomplishing this objective would also be within the scope of the invention. The various dimensions of the devices are not critical in the sense that slight deviation therefrom will produce a marked difference in behavior. The differential between the slots 26 and 28 should be maintained as small as possible and, moreover, because of the slots 26 and 28, the actual length of the split waveguide section should be maintained short in accordance with conventional theory. The type of element which is to be mounted in the split waveguide also does not form a portion of this invention, which is defined in the following claims.

I claim:

1. A device for mounting an element across the short dimension of a four-walled rectangular waveguide such that the element is substantially transverse to the widewalls of said waveguide, and wherein a voltage is to be applied across said element, comprising a split waveguide having first and second sections, said first and second sec tions being electrically insulated from each other and separated by straight longitudinal slots oifset from each other a small distance so as not to appreciably interrupt the longitudinal current flow in the walls of said split waveguide, means for electrically connecting said mounted element to each of said waveguide sections, means for physically connecting the ends of said split waveguide to respective first and second waveguides so as to form a continuous waveguide comprising said split waveguide and said first and second waveguides, and means for electrically insulating said split waveguide from said first and second waveguides.

2. A device according to claim 1, wherein said slots are offset by an amount less than ten percent of the longer dimension of said split waveguide as measured internally of the waveguide.

3. A device according to claim 2, wherein said means for connecting comprises respective choke joints for connecting the ends of said split waveguide to adjacent ends of said first and second waveguides.

4. A device according to claim 3, wherein said means for electrically insulating comprises a layer of insulation over the outer surface of each of said choke joints.

References Cited UNITED STATES PATENTS 2,860,244 11/1958 Crowley 333-98 3,311,852 3/1967 Giller 333-98 ELI LIEBERMAN, Primary Examiner. L. ALLAHUT, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,409,849 November 5, 1968 Donald Neuf It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 17, "fragmentary" should read frequency Signed and sealed this 10th day of March 1970.

(SEAL) Attest:

Attesting Officer WILLIAM E. SCHUYLER, JR. 

